This invention is related to emergency braking systems for vehicles, especially heavy work vehicles, of the type having emergency brakes in addition to the service brakes used for normal operation and, more particularly, to a hydraulic control system for the emergency brakes which provides a smooth yet complete engagement thereof.
It is known to provide vehicles with spring-apply, pressure-release service brakes, for example on highway trucks. Such brakes would also appear to be extremely useful in separate emergency braking systems in vehicles due to their fail-safe nature, since they mechanically engage in the absence of release pressure, and since they may also be used as parking brakes when the engine is not running and may have been so used especially for the latter purpose. However, unlike service brakes, emergency brakes are rarely applied gradually. Rather, the vehicle operator is usually reacting to an emergency situation and suddenly jams them on. Alternatively, the brakes might be applied automatically if hydraulic pressure were suddenly lost in the vehicle. The sudden application of full braking force is undesirable from a operator comfort and safety standpoint. At the same time, the load must be applied quickly and completely under emergency conditions.